Having determined the structure of crystals of deoxy sickle cell hemoglobin (Beta 6 glu yields val, one crystal form) at 3A resolution and deoxy Hb C (Beta 6 glu yields lys, two crystal forms) at 4.5 and 5.0A resolution, it is proposed to refine these models so their calculated diffraction patterns best agree with those experimentally observed. After refinement the intermolecular contacts will be examied and cataloged. We have prepared crystals of deoxy Hb A, S, and C all in the same lattice and space group. It is proposed to determine the degree to which these crystals are isomorphous. The crystals of deoxy Hb C are resistant to X-ray damage, grow readily and diffract very well. It is proposed to work out their structure at a resolution better than 2.5A. Hemoglobins Vancouver, Mobile and Korle Bu all are modified at Beta 73 asp, a residue involved in the sickling reaction. It is proposed to determine the structures of these hemoglobins and to examine the intermolecular contacts in these crystals. It is intended to start an investigation of liganded Hb H (Beta 4), whose physical chemistry is under intensive study here in the Biology Department in the laboratory of Dr. Gary Ackers.